||This article may be too technical for most readers to understand. (October 2012)|
ESPRESSO (Echelle SPectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations) is a new third-generation, high-resolution, fiber-fed and cross-dispersed echelle spectrograph (R = 140,000) for the visible wavelength range (350 nm – 720 nm), for the European Southern Observatory's Very Large Telescope (VLT). Its main feature is the spectroscopic stability and the radial velocity precision. With its very high spectroscopic precision, it will be able to detect Earth-like planets. For example, our Earth induces a radial-velocity variation of 9 cm/s on our Sun. ESPRESSO will build on the foundations laid by the hugely successful High Accuracy Radial Velocity Planet Searcher (HARPS) instrument at the 3.6-metre telescope at ESO’s La Silla Observatory. ESPRESSO will benefit not only from the much larger combined light-collecting capacity of the four 8.2-metre VLT Unit Telescopes, but also from improvements in the stability and calibration accuracy that are now possible (for example, laser frequency comb technology).
The requirement is to reach 10 cm/s, but the aimed goal is to obtain a precision level of a few cm/s. This would mean a large step forward over current radial-velocity spectrographs like ESO's HARPS. The highly successful HARPS instrument can attain a precision of 97 cm/s (3.5 km/h), with an effective precision of the order of 30 cm/s, making it one of only two instruments worldwide with such accuracy. The ESPRESSO would greatly exceed this capability making detection of earth-like planets from ground based instruments possible. Installation and commissioning of ESPRESSO at the VLT is foreseen in 2016.
The instrument is capable of operating in 1-UT mode (using one of the telescopes) and in 4-UT mode. In 4-UT mode, in which all the four 8-m telescopes are connected incoherently to form a 16-m equivalent telescope the spectrograph will reach extremely faint objects.
For example (for G2V type stars):
- Rocky planets around stars as faint as V ~ 9 in (in 1-UT mode)
- Neptune mass planets around stars as faint as V ~ 12 (in 4-UT mode )
- Earth-like planets around stars as faint as V ~ 9 (CODEX on the E-ELT) (2025)
- Schedule: First light on telescope: goal 2016
- Preliminary Acceptance Europe, October 2015
- Final Design Review, May 2013
- Preliminary Design Review, November 2011
- Kick off Meeting, January 2011
- Phase A Study Review Meeting, March 2010
The main scientific drivers for ESPRESSO are:
- The measurement of high precision radial velocities of solar type stars for search for rocky planets.
- The measurement of the variation of the physical constants (Search for possible variations of the constants of nature at different times and in different directions through the study of the light from very distant quasars).
- The analysis of the chemical composition of stars in nearby galaxies.
These science cases require an efficient, high-resolution, extremely stable and accurate spectrograph.
ESPRESSO is being developed by a consortium consisting of ESO and seven further scientific institutes:
- Centro de Astrofísica da Universidade do Porto (Portugal).
- Faculdade de Ciências da Universidade de Lisboa, CAAUL & LOLS (Portugal).
- INAF–Osservatorio Astronomico di Trieste (Italy).
- INAF–Osservatorio Astronomico di Brera (Italy).
- Instituto de Astrofísica de Canarias (Spain).
- Physikalisches Institut der Universität Bern (Switzerland).
- Université de Genève (Switzerland).
Comparison between ESPRESSO and CODEX
|Telescope||VLT (8m)||E-ELT (39m)|
|Sky aperture||1 arcsec||0.80 arcsec|
|λ coverage||350–730 nm||380–680 nm|
|λ precision||5 m/s||1 m/s|
|RV stability||< 10 cm/s||< 2 cm/s|
(D = 16 m)
with RV = 1 m/s
Radial velocity comparison tables
|Super-Earth (5 M⊕)||0.1||1.4 m/s|
|Alpha Centauri Bb (1.13 ± 0.09 M⊕)||0.04||0.51 m/s||(1)|
|Super-Earth (5 M⊕)||1||0.45 m/s|
|51 Pegasi b||Hot Jupiter||0.05||4.23 days||55.9||First-generation spectrograph|
|55 Cancri d||Gas giant||5.77||14.29 years||45.2||First-generation spectrograph|
|Jupiter||Gas giant||5.20||11.86 years||12.4||First-generation spectrograph|
|Gliese 581c||Super-Earth||0.07||12.92 days||3.18||Second-generation spectrograph|
|Saturn||Gas giant||9.58||29.46 years||2.75||Second-generation spectrograph|
|Alpha Centauri Bb||Terrestrial planet||0.04||3.23 days||0.510||Second-generation spectrograph|
|Neptune||Ice giant||30.10||164.79 years||0.281||Third-generation spectrograph|
|Earth||Habitable planet||1.00||365.26 days||0.089||Third-generation spectrograph (likely)|
|Pluto||Dwarf planet||39.26||246.04 years||0.00003||Not detectable|
MK-type stars with planets in the habitable zone
- CORALIE spectrograph
- SOPHIE échelle spectrograph
- ELODIE spectrograph
- List of extrasolar planets
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- Pepe, F.; Molaro, P.; Cristiani, S.; Rebolo, R.; Santos, N. C.; Dekker, H.; Mégevand, D.; Zerbi, F. M.; Cabral, A. et al. (January 2014). "ESPRESSO: The next European exoplanet hunter". Astronomische Nachrichten 335 (1): 8–20. arXiv:1401.5918. Bibcode:2014arXiv1401.5918P. doi:10.1002/asna.201312004.
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